Search for Muon-to-Electron Conversion with the COMET Experiment

Abstract

Charged Lepton Flavor Violation is expected to be one of the most powerful tools to reveal physics beyond the Standard Model. The COMET experiment aims to search for the neutrinoless coherent transition of a muon into an electron in the field of a nucleus. Muon-to-electron conversion has never been observed, and can be, and would be, clear evidence of new physics if discovered. The experimental sensitivity of this process, defined as the ratio of the muon-to-electron conversion rate to the total muon capture rate, is expected to be significantly improved by a factor of 100 to 10,000 in the coming decade. The COMET experiment will take place at J-PARC with single event sensitivities of the orders of 10−15 and 10−17 in Phase-I and Phase-II, respectively. The ambitious goal of the COMET experiment is achieved by realizing a high-quality pulsed beam and an unprecedentedly powerful muon source together with an excellent detector apparatus that can tolerate a severe radiation environment. The construction of a new beam line, superconducting magnets, detectors and electronics is in progress towards the forthcoming Phase-I experiment. We present the experimental methods, sensitivity and backgrounds along with recent status and prospects.

Study of cLFV with ℓiℓjγγ effective vertex

“…The target sensitivity of the MEG II experiment for µ → eγ will be O(10 −14 ) [29], and in the long term, it is widely expected that µ → e conversion in nuclei experiments will reach sensitivities O(10 −18 ) [27,30,31] or lower. Therefore, in the future the more stringent constraints on the low-energy dimension-7 operators, in the µ − e sector, will be provided by µ → e conversion in nuclei.…”

Lepton Flavour Violation Tests of Type II Seesaw Leptogenesis

“…The upcoming COMET experiment [26,104] is aiming to improve upon this limit to the following sensitivity,…”

“…In each Figure, the Dotted lines subtending Red regions and Dashed lines subtending Green regions denote the projected experimental sensitivity of the future COMET (µ to e conversion in Nuclei) and Mu3e (µ → 3e) experiments [26,101], respectively. The projected sensitivity of a future 100 TeV collider is given by the orange region, which will be able to probe the mass of the triplet Higgs up to 4 TeV at the 5σ level [105].…”

“…Searches for each of these processes complement each other through their varied dependencies on the triplet Higgs mass, neutrino oscillation parameters, CP violating phases, mass ordering, and lightest neutrino mass. Future experiments such as Mu3e [25] and COMET [26], will allow for vastly improved sensitivities over current constraints, allowing a new probe of the properties of the leptonic sector, and subsequently High Scale Leptogenesis. In this context, it is integral to determine the predicted signatures of the Type II Seesaw Leptogenesis Scenario at these upcoming experiments.…”

“…Figure 5. Comparison plot of the maximum m ∆ probed by µ to e conversion in Ti nuclei tests at the SINDRUM experiment[103] (Dashed) and at the upcoming COMET experiment[26] (Solid) for different sets of neutrino CP phases (δ CP , α 21 , α 31 ) and varying lightest neutrino mass, in the IO scenario. All other parameters are given by the best fit parameters in Table1.…”